1. Field of the Invention
The present invention relates to an electronic apparatus, a method of controlling the same, and a storage medium, and more particularly to an electronic apparatus equipped with a touch panel or a touch sensor as a user interface.
2. Description of the Related Art
In general, in an electronic apparatus, such as a personal computer, a PDA (personal digital assistant), or a cellular phone, a touch panel or a touch sensor (hereinafter generically referred to as the “touch operation section”) as a user interface.
Differently from a so-called mechanical button, the touch operation section suffers lack of feeling of an operation, such as a push feeling, caused by application of pushing pressure. This sometimes makes it difficult for a user to determine whether or not a touch operation by the user is accepted by the electronic apparatus. To eliminate this inconvenience, for example, there has been known a method of notifying the user of acceptance of a touch operation using sound and vibration (see Japanese Patent Laid-Open Publication No. 2002-149312).
To notify the user that a user's touch operation has been accepted by the electronic apparatus without causing an odd sensation in the user, it is desirable to generate notification sound instantly after the touch operation.
In general, however, a sound generation circuit installed on the electronic apparatus often uses a PLL (phase locked loop) circuit as a circuit for generating a sound sampling clock. Further, it is known that it takes a predetermined time period to start the PLL circuit.
The PLL circuit feedback-controls a voltage controlled oscillator such that a phase difference between a reference signal and an output from the voltage controlled oscillator (referred to as the “oscillation output”) is constant. In the PLL circuit, the voltage controlled oscillator is controlled according to a voltage indicated by a difference signal representing a phase difference between the reference signal and a signal generated by dividing the oscillation output, and the oscillation output synchronous with the reference signal is output from the voltage controlled oscillator.
At this time, an AC component of the difference signal is filtered out by a filter circuit, but to sufficiently remove jitter from the difference signal (input signal), the time constant of the filter circuit is inevitably increased. This makes slow the response characteristic of the filter circuit. In other words, it takes time for the filter circuit to respond, which causes a problem of an increase in time required to obtain the oscillation output synchronous with the reference signal after input of the reference signal.
In a case where such a PLL circuit is used, a time lag is caused between a time point when a touch operation by the user is received and a time point when notification sound is generated. On the other hand, to reduce the time lag between the touch operation and generation of the notification sound, if the PLL circuit is always energized, power is always consumed.